Highly Active Porous Carbon-Supported Nonprecious Metal-N Electrocatalyst for Oxygen Reduction Reaction in PEM Fuel Cells

摘要

As an alternative for platinum to reduce the cost, nonprecious catalysts for the oxygen reduction reaction (ORR) were synthesized by deposition of an Fe/Co—N_x composite onto nanoporous carbon black with ethylenediamine (EDA) as a nitrogen precursor. Two different nanoporous carbon supports, Ketjen Black EC300J (KJ300) and EC600JD (KJ600), were used as catalyst supports for the nonprecious catalysts. Rotating ring disk electrode measurements were carried out to investigate the ORR activity and selectivity of these catalysts. The results obtained from the optimized FeCo/EDA-carbon catalyst, using KJ600 as the support, showed improved onset and half-wave potentials and superior selectivity than that of the KJ300. Similarly, the catalyst showed good performance in the hydrogen-oxygen PEM fuel cell. At a cell voltage of 0.6 V, the fuel cell managed to produce 0.37 A/cm~2 with a maximum power density of 0.44 W/cm~2. A fuel cell life test at a constant voltage of 0.40 V demonstrated promising stability up to 100 h. The catalysts were characterized by X-ray diffraction, energy-dispersive X-ray spectrometry, and X-ray photoelectron spectroscopy. The characterizations indicated that pyridinic-type nitrogen of the nonprecious metal catalysts is critical for ORR catalytic activity and selectivity. These results suggest that a higher pore volume and surface area of the carbon support could lead to a higher nitrogen content, providing more active sites for ORR, and this type of catalyst has great potential used as a nonprecious PEM fuel cell catalyst.